This invention relates generally to antenna arrays and more particularly to apparatus for testing active antenna arrays.
As technology improves, electrical systems become more and more complicated. This complexity makes it difficult to know if the system is operating properly and to diagnose failures. To make systems more maintainable, built in test (or "BIT") circuitry has been added to systems. The BIT circuitry monitors the operation of the system and reports when failures occur.
An inherent limitation of BIT circuitry is that the BIT circuitry adds further complexity to the system. If the BIT circuitry is too complicated, it can make the system harder, rather than easier, to maintain. For example, there would be no benefit to adding three components of BIT circuitry, each having a mean time between failures of 100 hours, to test a component with a mean time between failures of 50 hours. If the BIT circuitry indicated a failure, it would more likely be due to a failure in the BIT circuit than in the component being tested. Accordingly, it is desirable for BIT circuitry to be as simple as possible.
One system in which BIT could be of benefit is a phased array transmitter. BIT circuitry for such systems has generally been limited to measuring the level of the signal applied to each antenna element. This signal level can be easily measured by coupling a portion of the signal at the input of the antenna element to a test circuit which measures its level.
Measuring the level of the signal at the input of the antenna provides useful information about a transmitter system. However, to more fully check the operation of the transmitter, other measurements can be taken. For example, it is important to know the effective radiated power (ERP) from any antenna element. Additionally, in a phased array system, it is important to check the operation of phase shifters used to control the phase of the signal transmitted from each antenna element.